Cardanol-like co-surfactants solubilized in pegylated micelles keep their antioxidant activity and preserve polyethylene glycol chains from oxidation

Pegylated (PEG) surfactants are widely used for material and biomedical applications. Their use, however, is limited by the radical-mediated oxidation of the OCH2 moieties by atmospheric oxygen, that produces unwanted and toxic products such as hydroperoxides. We show herein that cardanols, natural alkylphenols byproducts of cashew nut processing, are able to form stable co-micellar systems with a model PEG-containing surfactant (Triton X-100, i.e. p-tert-octylphenoxy polyethylene-glycol ether) and display antioxidant activity toward PEG degradation by O2. The cardanols investigated were 6-tert-butyl-3-pentadecylphenol and 4-hydroxy-6-tert-butyl-3-pentadecylphenol. The ability of cardanols to form co-micelles with Triton X-100 was investigated by determining the critical micelle concentration (CMC), the microviscosity, the polarity and the aggregation number. The antioxidant activity of cardanol derivatives in dispersed systems of Triton X-100 was evaluated by studying the reaction with DPPH radical and the protecting activity toward the peroxidation of the polyethylene-glycol tails. The obtained activity of cardanol derivatives was similar or better than that of commercial synthetic antioxidants BHT (2,6-di-tert-butyl-4-methylphenol) and DTBQ (2,5-di-tert-butylhydroquinone), taken as reference, under the same conditions. This study enlightens the ability of hydrogenated cardanol derivatives to act as radical-trapping agents and/or as protective co-surfactants toward the oxidative degradation PEG-coated nanoaggregates used in food and drug science.